Expandable intraluminal endoprosthesis

ABSTRACT

An expandable intraluminal endoprosthesis including a tubular member ( 1 ) a first diameter which permits intraluminal delivery of the member into a lumen of a body passageway, particularly a blood vessel. The tubular member ( 1 ) is capable of acquiring a second, expanded and deformed diameter upon the application from the interior of the tubular member of a radially outwardly extending force, which second diameter is variable and dependent on the amount of the force applied to the tubular member. Such a tubular member may be expanded and deformed to expand the lumen of the body passageway. The wall of the tubular member includes a substantially continuous structure ( 2 ) of mutually staggered undulations. This structure has been separated from a tube wall and exhibits at lest one pattern which advances substantially helically along a longitudinal axis of the tubular member. Connection elements within the structure connect adjacent undulations to each other. These connection elements are an integral extension of the undulations thereby interconnected.

The present invention relates to an expandable intraluminalendoprosthesis comprising a tubular member having a first and second endand a wall surface disposed between said first and second end, the wallhaving a substantially uniform thickness and having a first diameter ina first, unexpanded state which permits intraluminal delivery of themember into a lumen of a body passageway, particularly a blood vessel,which member is capable of acquiring a second diameter in an expandedand deformed state upon the application from the interior of the tubularmember of a radially outwardly extending force, which second diameter isvariable and dependent on the amount of said force applied to thetubular member, whereby the tubular member may be expanded and deformedto expand the lumen of the body passageway. More particularly theinvention relates to an expandable intraluminal vascular endoprosthesiswhich is especially useful for repairing or reconstructing blood vesselsnarrowed or occluded by a disease. Commonly this kind of medical deviceis referred to as vascular stent or graft.

Stents are prosthetic devices which are implanted inside a lumen inorder to provide support for its wall and to assure an undisturbed flowthrough the lumen. This is particularly important in the field ofangioplasty which is concerned with the repair and reconstruction ofblood vessels. In that particular field stents are implanted within thevascular system to reinforce collapsing, partially occluded, weakened,or abnormally dilated sections of blood vessels. More generally,however, stents can be used inside the lumen of any physiologicalconduit or duct including the arteries, veins, bile duets, the urinarytract, alimentary tracts, the tracheobronchial tree, a cerebral aqueductand the genitourinary system. Moreover stents can be used inside luminaof animals besides humans.

Generally two types of stents may be distinguished. First there areself-expandable stents which automatically expand once they are releasedto assume a permanent deployed, expanded state. These stents expand to adefined diameter and are unable to remodel the true vascular anatomyover lengths greater than 2 cm. Their drawback is that the physicianneeds to place the right device and thereby has to rely on informationderived from fluoro and angiographic equipment. A second type of stentsconcerns the so-called balloon expandable stents which generally involvea tubular member capable of receiving a balloon of a balloon-tippedcatheter by means of which it may be deployed. The present inventionparticularly pertains to this second kind of stents.

A common procedure for implanting a balloon-expandable stent in a bloodvessel involves mounting the stent in its unexpanded, crimped state on aballoon-tip catheter of a suitable delivery system. The catheter is thenslipped through an incision in the vessel wall and down the length ofthe vessel until it is positioned to bridge the diseased or narrowedportion of the vessel. The stent is then expanded with the aid of theballoon-catheter against the internal wall of the vessel. This may bedone after the vessel has been predialated and it has been determinedthat a stent is necessary. Alternatively the vessel could be dilated bythe stent itself while the latter is expanded by means of the balloon.It both cases the stent will maintain its deployed, expanded form oncethe balloon is evacuated and the catheter retracted again in order toprovide a permanent support for the blood vessel concerned.

A wide overview of vascular stents which are nowadays available is givenin the Handbook of Coronary Stents by Patrick W. Serruys et al. of theRotterdam Thoraxcentre Interventional Cardiology Group. This overviewdescribes at page 21 ff. the so called Palmaz-Schatz™ stent as the goldstandard in the field of stents. This stent concerns a number ofconsecutive slotted tubes of stainless steel which are mutuallyconnected by means of one or more bridges. Although this stent is mostwidely used and tested in practice, it has been implanted in over 600000patients all over the world, it still suffers from a number ofdrawbacks. The main drawbacks have to do with the stent-to-vessel-ratiouniformity and crimped as well as deployed flexibility. Thestent-to-vessel-ratio involves the degree to which the vessel issupported by the stent in its expanded state and should not only behigh, but preferably also uniform throughout the length of the stent.However, due to the inevitable bridges between adjacent tubes of thePalmaz-Schatz™ stent, there will be a bare area between adjacentsegments of the stent once it has been deployed giving rise to adecreased and even poor stent-to-vessel-ratio at these locations. Theother drawback concerns the rather high rigidness of the stent segmentsin their crimped and deployed state. As a consequence the stent has onlya limited flexibility which hinders the delivery of the stent to itsintended position inside the body. The poor deployed flexibility of thisstent gives rise to a straightening of the vessel over segments longerthan typically 2 cm which appears to be a primary cause for late termrestenosis of the stented area. Typically this occurs after about 6months after surgical post procedural.

A balloon expandable stent with a highly uniform stent-to-vessel ratioas well as an excellent flexibility in its crimped state is described atpage 63 ff. of the same reference and concerns the Cordis CoronaryStent. This device is composed of a single piece of tantalum (Ta) wire.The wire is wrapped to form a continuous sine wave and helically woundalong a longitudinal axis. Both ends of the wire are weld terminated. Asimilar device was presented at the annual symposium of the RadiologicalSociety of North America (RSNA) 11/95. This peripheral stent embodimentincorporates intermediate welds, patterned through the length of thestent. This device contains adjacent helical turns of the wire which arewelded together at adjoining locations and exhibits a highly regulardistribution of the wire along the length of the device. Its properties,such as crimped profile and stent-to-vessel ratio, are uniform over itslength both in the crimped and deployed states. However, because of itsconstitution this device offers only a poor design freedom when it comesto tailoring the design to add specific functionality and remove certaindrawbacks. Also the internal stress in the device once it has been woundhinders the provision of reliable welds between adjacent turns. Thesewelds as well as those to the ends of the wire moreover remain a weakpoint especially during expansion of the device.

It is an aim of the present invention to provide a balloon expandablestent which combines a high degree of uniformity and flexibility withexcellent design capabilities.

To this end an expandable intraluminal endoprosthesis of the kinddescribed in the opening paragraph according to the invention ischaracterized in that at least in said first unexpanded state at least apart of said wall of said tubular member comprises a substantiallycontinuous structure of mutually staggered undulations which has beenseparated from a tube wall, in that said substantially continuousstructure comprises at least one pattern which advances substantiallyhelically along a longitudinal axis of said tubular body and in thatsaid structure comprises connection elements connecting adjacentundulations, which connection elements are an integral extension of theundulations which they connected.

The structure making up the wall of the tubular member may be separatedfrom a hollow tube by means of for instance laser cutting or a similartechnique available to a skilled person. In this manner a substantiallystress-free structure may be created incorporating a substantiallyhelically advancing pattern which can be highly uniform and flexiblethroughout the length of the device but still facilitates unimpaireddesign freedom to tailor the pattern to meet additional functionalityand to remove specific drawbacks. Moreover as the connecting elementsare likewise separated from the tube as the rest of the structure andconsequently are entirely integral with said structure the drawbacksassociated with the welds in the prior art device may be avoided. Thesubstantial helical pattern within the structure may be designed toform, upon deployment, a substantially continuously advancing spine as akind of backbone of the device.

A specific embodiment of the endoprosthesis according to the inventionis characterized in that said structure comprises a continuous filamentwhich is separated from a tube wall, in that said adjacent undulationsare staggered in a substantially helical configuration advancing along alongitudinal axis of the tubular body to form one of said at least onesubstantially helical pattern within said structure, and in that a firsthelical turn of said filament around said longitudinal axis of saidtubular member is connected to an adjacent second such turn of saidfilament by means of at least one of said connection elements, being anintegral extension of said filament. This embodiment to large extendcompares to the Cordis Coronary Stent referred to above, without howeversharing the above described drawbacks of that device.

In order to improve on flexibility in a compressed as well as in adeployed state of the device a further specific embodiment of theendoprosthesis is according to the invention characterized in thatadjacent turns of said filament are connected to one another by means ofa number of connection elements less than the number of undulations insaid turns. Due to the fairly unlimited design freedom in the device ofthe invention, the number of interconnections between adjacent turns maybe adapted freely to suit the flexibility of the device. The lessconnection between adjacent turns, the more flexible the device will be.Said design freedom moreover allows a variation of the number ofinterconnections between adjacent turns within the same device to suitan optimal behaviour.

In a preferred embodiment an endoprosthesis is according to theinvention characterized in that said structure comprises a number ofturns of said filament whereby the connection elements to subsequentturns are radially shifted to form at least one further substantiallyhelical pattern of said at least one substantial helical pattern withinsaid structure. In this manner a kind of primary framework structure maybe obtained which supports the vessel wall while maintaining deployedflexibility. More specifically a preferred embodiment of theendoprosthesis according to the invention is characterized in that atleast a portion of the structure comprises a number of connectionelements which are substantially equally divided in each turn of saidfilament and in that connection elements in successive turns arehelically shifted by approximately one undulation pitch distance. Byshifting the connection elements substantially a full pitch distance astructure is realized in which successive connection elements are linkedto each other by substantially a full undulation of said first pattern.This undulation introduces significant slack and expandable diameterwithin the helical spine created by the interlinked connection elementswhich allows a very gradual expansion of the device transverse to itslongitudinal direction. This reduces so called foreshortening which is alongitudinal shrinking of the device as it is expanded and wouldotherwise limit the effective range of the device.

A further specific embodiment of the device according to the inventionis characterized in that at least some of the connection elementscomprise a strut diagonally interconnecting a first side of a firstadjoining undulation to an opposite side of a second adjoiningundulation, the strut being entirely integral with said adjoiningundulations and having a direction different to the helical direction ofsaid one substantial helical pattern within said structure. Upondeployment, this structure will create a kind of spine which runs over aseries of connection elements in a different, or even contra-, helicaldirection compared to that of said one substantially helical pattern.Such multiple-helix structure is capable of withstanding a significanthoop strength whilst still being flexible and conformal to the naturalvessel wall.

In a still further embodiment an endoprosthesis is according to theinvention characterized in that the connection elements to subsequentturns are radially shifted by approximately one undulation pitchdistance. Due to this regular pattern of connection elements one or morecontinuous, helically turning spines will be obtained in the deployedstale of the device, formed by subsequent struts and the respectivesides of the undulations they interconnect. These spines may form ascaffolding lattice which uniformly supports the vessel wall whilemaintaining deployed flexibility in order to be as conformal as possiblewith the natural form of the vessel concerned. It has been found thatespecially lack of the latter, resulting in a unnatural straightening ofthe vessel over a certain length, is a primary cause for late termrestenosis of the stented segment. Due to the deployed flexibility andits highly conformal deployed shape this still further embodiment of theinvention aims to avoid this problem.

To further improve on flexibility while maintaining hoop strength, i.e.the ability to withstand inwardly directed radial forces, a furtherspecific embodiment of the endoprosthesis according to the invention ischaracterized in that the first side of said first undulation, saidopposite side of said second undulation and said strut have a firstfilament width and in that the opposite side of said first undulationand the first side of the second undulation have a second filamentwidth, the first filament width being larger than the second filamentwidth. The inventor has recognized that said second filament width maybe made smaller than said first filament width, thus gainingflexibility, without deteriorating the strength of the device andparticularly its radial hoop strength.

In a further specific embodiment the endoprosthesis according to theinvention is characterized in that said strut connecting opposite sidesof adjoining undulations of subsequent turns have a substantiallyS-shaped structure. Such a double curved structure of the connectionelements creates more slack between mutually interconnected undulationsallowing more expansion as well as an improved stent to vessel ratio atsaid area once the prosthesis has been deployed.

A still further preferred embodiment of the endoprosthesis according tothe invention is characterized in that the connection elements eachcomprise two intersecting struts which are entirely integral with eachother and with the adjoining undulations which they connect. Theinventor has recognized that on deployment of the device such aninterconnection element will first rotate around its central axis beforethe entire force applied pulls axially on the point of inter section. Asa consequence a certain stress relief is incorporated in the devicewhich allows for a smaller filament width. This does not only add to theflexibility of the device but also leads to a more favourableradio-opacity. Moreover, the intersecting struts leave a substantiallyunchanged scaffolding area or footprint upon deployment of the structurethereby improving on the eventual stent-to-vessel ratio of the devicecompared to a connection element which will almost entirely stretch upondeployment.

The design freedom gained by the endoprosthesis according to theinvention appears fairly unlimited and can be applied to preciselytailor the properties of the device to specific requirements. Not onlythe form, number and the location of connection elements but also thefilament width and form of particular parts may be adapted in thissense. As an example, a further specific embodiment of the invention ischaracterized in that the undulations in said filament have a firstmutual pitch in a first of said turns of said filament and a secondmutual pitch in a second of said turns, the first and second pitch beingdifferent from each other. Varying the mutual pitch of the undulationswill generally give rise to more or less flexibility in combination withless or more vessel support at the zones concerned.

A still further embodiment of the endoprosthesis according to theinvention is characterized in that at least a part of at least oneundulation in at least one turn of said at least one substantiallyhelical pattern has an increased amplitude, while at least the adjoiningpart of an adjoining undulation in an adjacent turn has acorrespondingly decreased amplitude. In this case the mechanicalproperties of the device and especially the manner of deployment as wellas the stent-to-vessel ratio may be tailored by offsetting the pointwhere adjacent undulations meet.

More specifically a further embodiment of the endoprosthesis accordingto the invention is characterized in that a first pair of adjacentundulations of said structure is connected by means of a firstconnection element, in that a second pair of adjacent undulation of saidstructure is connected by means of a second connection element, in thatin between said first and second pair of connection elements at leastone undulation of an intermediate pair of undulations has an increasedamplitude, to bridge at least part of the length of said first andsecond connection element. In this case the inevitable length of theconnection elements between adjacent turns of the device is at leastpartly compensated by the increased amplitude of said at least oneundulation, leading to a more uniform deployed stent-to-vessel ratio.

Besides or even instead of being formed by a series of substantiallyhelically staggered undulations, a substantially helically advancingpattern within the structure may also be created by the connectionelements in themselves. In this respect, a specific embodiment of theendoprosthesis according to the invention is characterized in that saidstructure comprises at least one series of connection elements which aresubstantially regularly distributed over at least part of the length ofsaid tubular body and in that successive connection elements within saidat least one series are radially shifted to form one substantiallyhelical pattern of said at least one substantially helical patternwithin said structure. More specifically, a preferred embodiments of theendoprosthesis according to the invention is characterized saidsuccessive connection elements are mutually connected by an elongatedmember which has a greater length than the linear distance between saidconnection elements in said first unexpanded state of the structure, inorder to impart radial expandability to the structure.

In this manner a helically advancing spine is realised throughout atleast a part of the device which adds to the scaffolding lattice of thestructure, especially in the deployed state of the device. One or evenmore of such spines may give the device a considerable hoop-strength andsupporting capability, without depriving the structure of its crimped aswell as deployed flexibility. The greater length of the elongated memberadds expandable diameter to the individually connected connectionelements, imparting additional slack within the structure, an improvedexpandability and less fore-shortening on the device. This additionalcircumference allows for side branch access greater than the maximumexpanded diameter of the stent along the longitudinal axis. In thisrespect, a specific embodiment of the endoprosthesis according to theinvention is characterized in that said elongated member comprises asubstantially S-curved bent. The S-curved members are situated along thespiral helix equidistantly spaced, along the longitudinal axis of thetubular body, and primarily allow the device to uniformly expand outradially enabling the structure to orient itself into a helicalstructure upon deployment. In a more particular embodiment the S-curvedbent is orientated substantially parallel to the longitudinal axis ofthe tubular body, which allows the member to uniformly expandperpendicular to said axis. This prevents the device from twisting androtating on the balloon-catheter, or the like, as the device undergoesexpansion.

The endoprosthesis according to the invention may have a uniformstructure throughout the device. A preferred embodiment of the device ishowever characterized in that the tubular body comprises a centralportion, two outer portions at opposite ends of said tubular body and atleast one intermediate portion in between the central portion and eachof said end portions, the different portions being designed according totheir specific function in the device. This embodiment is based on therecognition that different requirements may have to be imposed ondifferent parts of the endoprosthesis to precisely meet the specificfunction or desired behaviour of the part concerned while the device iseither unexpanded, expanded or in a transition between the unexpandedand expanded state. The present invention provides for a device in whichthis kind of tailoring may be implemented.

More particularly a further embodiment of the endoprosthesis accordingto the invention is characterized in that at least in one of the twoouter portions of the tubular body the undulations in said structurehave a gradually decreasing amplitude whether or not in combination witha changing pitch or filament width in order to render a free end of saidportion substantially transverse to the longitudinal axis of said body,at least in said first unexpanded state of said structure. Such asquare-like tubular end of the endoprosthesis prevents an undesiredcantilever protrusion of the last turn which otherwise could harm thewall of the lumen while the device is being navigated to its intendedposition. Moreover this structure improves the mechanical bond betweenthe endoprosthesis and the balloon of the catheter used to manipulatethe device within the body. The square end is created by graduallydecreasing the amplitude and changing the pitch of the last fewundulations until there is a final smooth transition forming the desiredsquare end. Modifications of the filament width at this area may furtherimprove this part's behaviour.

A still further embodiment of the endoprosthesis according to theinvention is characterized in that said central portion of the tubularbody comprises a first number of connection elements per full helicalturn of said at least one substantially helical pattern within saidstructure, in that at least one of said intermediate portions comprisesa second number of connection elements of the structure per full helicalturn of said at least one substantially helical pattern within saidstructure, and in that the first number of connection elements issmaller than said second number of connection elements imparting adifference in flexibility between both portions of the tubular body.More precisely, the central portion will exhibit more flexibility thanthe intermediate portions due to the lower number of interconnectionsbetween adjacent turns. To accommodate this difference within thestructure, a specific embodiment of the endoprosthesis according to theinvention is characterized in that the central portion and anyone ofsaid intermediate portions are separated from each other by atransitional portion in order to smoothly change the number ofinterconnections between adjacent turns from the first number to thesecond number of connection elements per full helical turn of saidpattern.

In a more specific embodiment the endoprosthesis according to theinvention is characterized in that adjacent turns in said centralportion comprise a number of connection elements which are equallydivided and in that connection elements in subsequent turns arehelically shifted by approximately one undulation pitch distance. Forexample six adjoining helical segments with three equally spacedconnection elements, situated approximately 120° with respect to oneanother or six opposing helical segments with two equally spacedconnection elements situated approximately 180° with respect to oneanother. This specific design yields the most flexible structure in thecentral region, both crimped and deployed. Once deployed, the structurewill orient itself in line with the helical lattice structure which itforms, exhibiting three intertwining continuous lattice legs within theintermediate region and only two of those legs in the central region.The intermediate region will posses more stiffness in order tocounteract the balloon expansion, known as the “dog bone effect”, whichcauses the ends of the device to flare prematurely prior to thedeployment of the central section and which results in an undo amount offoreshortening upon expansion. Moreover the intermediate regions serveas a relief between the end portions and the central region of thedevice.

The present invention will now be further described in more detail withreference to the following figures in which like elements are providedwith the same reference numerals.

FIG. 1 shows an isometric view of an embodiment of an expandableintraluminal endoprosthesis in accordance with the present invention;

FIG. 2 is a plan view of the endoprosthesis of FIG. 1;

FIG. 3 shows alternative embodiments of interconnection elements to bein a device according to the invention;

FIG. 4 is an enlarged view of an end portion of the endoprosthesis ofFIG. 1;

FIG. 5 shows an isometric view of a second embodiment of an expandableintraluminal endoprosthesis in accordance with the present invention;

FIG. 6 shows a plan view of the device of FIG. 5 in a unexpanded state;and

FIG. 7 is a plan view of the device of FIG. 5 in a expanded, deployedstate.

The figures are drawn merely schematically and not to scale. Moreparticularly some dimensions may be exaggerated to more clearly pointout one or more aspects of the present invention. Like parts thedrawings are indicated as much as possible by like reference signs.

FIG. 1 gives a isometric view of an expandable intraluminalendoprosthesis according to a specific embodiment of the presentinvention. The endoprosthesis, hereinafter briefly referred to as stent,comprises a tubular member 1 which has been separated out of a tubularbody of a suitable bio-compatible material. As such for instance highgrade stainless steel (SST), a nickel-titanium based alloy referred toas Nitinol (NiTi), several cobalt based alloys and a Niobium-Titanium(NbTi) based alloy qualify. In this case the latter material may bechosen because of its excellent mechanical strength, corrosionresistance and radiopaque fluoroscopic signature. In the first,unexpanded state shown, the tubular member 1 is drawn with a firstdiameter d which permits delivery of the member into a lumen of a bodypassageway, particularly a blood vessel. The member 1 is capable ofacquiring a second, expanded and deformed diameter upon the applicationof a radially outwardly extending force from its interior, usually bymeans of a balloon-catheter. This second diameter is variable anddependent on the amount of force applied. Inevitably the member willshow a certain amount of recoil which means that the device will retractmore or less after the balloon has been evacuated. Accordingly thesecond diameter will be slightly smaller than the diameter to which thestent has been expanded. Nevertheless the tubular member may be expandedand deformed to expand the lumen of the body passageway to again assurean undisturbed flow through the lumen, like a blood vessel.

The wall of the stent comprises a substantially continuous structurewhich in this example consists of a continuous filament which has beencut out from the tube wall in a substantially helical fashion with awidth between about 0.10 and 0.17 mm. This may be done by means of lasercutting, electrochemical etching, electromechanical discharge or anyother suitable technique preferably followed by a suitable surfacetreatment, like etching to deburr and or round off possible sharp edges.In this example a tubular body with an internal diameter of about 3.0mm, a wall thickness of about 1.0 mm and a length of about 30 mm hasbeen chosen as a starting material. However other dimensions arclikewise feasible within the scope of the present invention.Particularly the length may be adapted to the diseased part of the lumento be stented in order to avoid the necessity of separate stents tocover the total area. The filament-structure comprises a number ofundulations 2 which are mutually staggered in helical pattern advancingaround a central longitudinal axis I-I of the device. In order to retaina coherent body subsequent turns A-H of the filament are interconnectedby means of one or more connection elements 31,32 which are entirelyintegral with the undulations thereby connected as they are cutaltogether from one and the same tubular body. To retain flexibility,both unexpanded as well as deployed, the number of connection elementsper helical turn is less than the number of undulations in said turn.This is further elucidated in FIG. 2 which gives plan view of the deviceas if it were cut open. As emerges quit clearly from this figure, theconnection elements 31 to subsequent turns are radially shifted by abouthalf undulation pitch distance ½L to form a helical pattern X-X, Y-Y.Once deployed, these patterns will expand to a helically turning spineswhich form a primary framework or scaffolding lattice of the deployedstent. This framework supports the vessel wall highly uniformlythroughout the device and moreover is capable of withstandingsubstantial inwardly directed radial forces, which is referred to as itshoop strength.

The lower drawing part of FIG. 2 shows a part of a central modularportion of the device in which successive turns of the filament areinterconnected by means of only two connection elements 31, which areshifted about 180° with respect to one another, while the upper partshows an end portion of the device together with an intermediate portionin which three equally spaced connection elements 31,32 interconnectadjacent undulations from successive turns of the filament with eachother. As a result the parent scaffolding lattice of the deployed devicewill be composed of only one helically advancing spline within thecentral region and will comprise two helically revolving spines withinthe other regions. Although the latter provides less flexibility, itleads to an improved adhesion to the balloon-catheter by which thedevice is guided through the lumen and moreover counteracts a so calleddog bone effect, which is a premature expansion at the tail ends of thedevice. The central portion of the device, i.e. the lower drawing part,on the other hand retains maximum flexibility and conformability due tothe smaller number of interconnections between adjacent undulationswithin this segment.

In this example two kinds of connection element are used, denoted 31 and32 respectively. Both types of connection elements feature a strut 3which is S-shaped and diagonally interconnects opposite sides ofadjacent undulation from successive turns of the filament in a helicaldirection different to that of the staggered undulations themselves, seealso FIG. 3E. These struts will be referred to as major struts as theyare part of the lattice spines described hereinbefore. The second typeof interconnection element 32 moreover features a second, S-shapeddiagonal 4 strut intersecting the first one, see also FIG. 3D. Due tothis shape an interconnection element of the second kind 32 will firststart to rotate around its central axis once the stent is being deployedwith only a limited force being exerted axially in the diagonal 3 of theconnection element. Only after the first diagonal 3 has become fully inline with the sides of the undulations it interconnects, it hits towithstand the entire force axially. This incorporated slack and stressrelief allows thinner strut width and filament width over the latticelegs which can be useful for decreasing the radio-opacity at this areaas well as improves its unexpanded, crimped as well as deployed,expanded flexibility. Moreover the support area covered by a connectionelements of this second kind will not decrease much upon deployment ofthe device. As a result a larger “scaffolding footprint” will remainafter deployment compared to any of the other types of connectionelements shown which all will stretch substantially upon deploymentleaving only the thin major strut 3 as “scaffolding footprint”.

Besides the types connection elements depicted in the drawing also othershapes are feasible, as the invention imposes hardly no limitation ofthe design of any part of the device including the shape of theinterconnections used. Examples of other shapes which couldadvantageously be used in a device according to the invention are shownin FIGS. 3A-3G. The connection elements of FIGS. 3A-3C merely comprise astraight strut 3 connection adjacent undulations, whereas the main strut3 of the connection elements shown in FIG. 3D-3F have a clearly S-curvedshape. This shape introduces more slack and expandability in thestructure. The longer this segment, the more slack and expandabilitythere is in the structure and especially in the spinal ladder created bythe connection elements in the eventual deployed device. A simpleformula can be derived from the expanded state, defining the relativeincrease of the strut length and the effect it has on the expansionrange of the device.

The major strut 3, i.e. the strut eventually forming part of the parentscaffold or framework of the device once it is deployed, is indicated inFIG. 3 by a dotted hatch. In a special embodiment this strut as well asthe undulation sides which it interconnects are given a first filamentwidth w₁ sufficiently large to withstand the axial forces imposedthereon during expansion of the device, whilst the other undulationsides and if applicable the other strut of the connection element aregiven a second filament width w₂, at least locally, to gain flexibilityand decrease radio-opacity. Specifically the filament width is modifiedin the central portion of the device to improve its overall flexibilitysuch that a first filament width w₁ of approximately 0.14 mm is takenwhereas the second filament width w₂ is reduced to about 0.11 mm.

In order to avoid a substantial disruption of the stent to vesselsupport by pairs of undulations from successive turns of the filamentwhich are not mutually interconnected by at connection element, theamplitudes of the undulations within such pair may be adapted to fillthe gap which would otherwise remain due to the inevitable length of aconnection element elsewhere in the structure. This is for instanceapparent from FIG. 2 where all adjacent peaks and valleys of pairs ofundulations out of successive turns which are not interconnectednevertheless adjoin one another. This is a result of the adapting theamplitude of at least one of the undulations within such pair ofundulations. This can imply that both, the peak and the valley have anincreased amplitude, that only one of those parts is enlarged, the otherpart remaining unchanged, or even that either the peak or the valley hasa increased amplitude while the other part has a decreased amplitude.Also in this respect, the designer has full freedom to tailor the stentdesign to allow optimal behaviour of the stent in its unexpanded state,expanded and/or transitional state.

The end portion of the device ends substantially transverse to thecentral axis of the device in order to avoid a cantilever usuallyassociated with a helix shape which could otherwise harm the wall of thelumen through which the stent is navigated. This end portion is shown inmore detail in FIG. 4. Its particular shape is obtained by graduallydecreasing the amplitude in the last few undulations and adapting theirmutual pitch. Due to the invention this may be done without introducingany stress in the device as the filament is simply cut in the desiredpattern. The deviating amplitudes and mutual pitch are best recognizedfrom the plan view of FIG. 2. The end modules exhibit a greaterstent-to-vessel ratio than the central and intermediate portions due tothe increased metal-to-surface-area in the expanded configuration. Themore complex structure of the end portions moreover give rise to agreater amount of foreshortening upon expansion, thus producing a moredense pattern yielding additional stent-to-vessel ratio.

A second embodiment of the device according to the invention is depictedin FIGS. 5-7. This device comprises a tubular body 1 and has beenmanufactured using similar techniques as the first embodiment, althoughin this case a more complicated structure has been created consisting ofmore than just a single, wrapped filament. However, like in the firstembodiment, the structure of the device is composed of a substantiallyhelical pattern of mutually staggered undulations 2, with connectionelements 33 interconnection some undulations from successive turns ofsaid pattern. The connection elements within this structure primarilycomprise two intersecting struts like the type reflected in FIG. 3D.

Different to the structure of the first embodiment, connection elements33 to subsequent turns of said pattern are shifted by about a full pitchdistance. As a result a full undulation 25 will link said connectionelements 33 to one another and as such creates an elongated member 25 inbetween the connection elements 33. Said elongated member formed by anintermediate undulation comprises a S-curved bent and is longer that thelinear distance between the interconnection elements thereby linked toeach other, at least in the crimped state shown in FIGS. 5 and 6. Thisimparts additional slack and considerable expandability to the spinalladders which are formed by such a series of linked connection elementsin the deployed state shown in FIG. 7. Moreover the orientation of theS-curved bents in said elongated members 25, which is substantiallyparallel to the longitudinal axis of the body at least in the crimpedstate shown in FIGS. 5 and 6, allows the member 25 to uniformly expandin a direction which is substantially perpendicular to said axis. Thisprevents the device from twisting and turning on the balloon-catheteronce it is being expanded.

Like in the first embodiment, also in this case said series ofinterlinked connection elements mutually shifted by a pitch distance,form further substantially helically advancing patterns within thestructure. Like the staggered undulations themselves, these furtherhelically revolving patterns will mature to helical spines runningthrough the structure once it is being expanded, see FIG. 7. Theseadditional spines however run in a different direction than the spinescreated by the undulations, indicated by the straight lines in FIG. 7,which results in an eventual structure with a considerable hoop strengthin combination with an excellent unexpanded and deployed flexibility. Asthe device of the invention allows for a very large design freedom,these aspects may be once more tailored throughout the device to fit thebest overall characteristics in each portion of the device.

Although the invention has been described hereinbefore with reference tomerely a few embodiments, it will be appreciated that the invention isfar more wide spread applicable. Within the scope of the invention manyother embodiments and variations are feasible for a skilledpractitioner. As such he may vary for instance the mutual pitch of a fewor more subsequent undulation with or without a variation of theamplitude in order to tailor the stent-to-vessel ratio and flexibilityat the area concerned. Also, additional modular portions individuallyrecognizable in the stent could be implemented in the stent in order toadd specific functionality. As such, a transitional portion might beinterposed between the relatively flexible central portion and the morestiff intermediate and end portion in order to alleviate the structuraltransition between those parts of the stent. Also the number ofconnection elements within a full turn of the helical pattern may beraised to introduce additional lattice spines to the deployed device,resulting in even a larger hoop strength and supporting capability ofthe device.

Likewise, the filament width as well as undulation shapes may be variedand adapted to suit specific required characteristics besides theflexibility and stent-to-vessel ratio. For instance, the foreshorteningof the device, i.e. the amount of length reduction upon expansion fromthe crimped to the deployed state of the device, its degree of recoil,its hoop strength as well as its radio-opacity. In any event the presentinvention provides the designer with the greatest amount of freedomconceivable.

Also the elongated members interlinking a series of connections elementslike in the second embodiment need not coincide with undulations of thepattern and can be introduced in the structure as separate elements.These members moreover need not necessarily comprise a full S-curvedbent or even no S-curved bent at all and may on the other hand consistof more than just one such bent. Also in this respect the designer hastotal freedom to tailor the device to his demands.

1-20. (canceled)
 21. A stent that expands under radial force from afirst diameter to a second diameter, the stent comprising: a firsthelical segment comprised of a plurality of filament segments arrangedto form a first repeating pattern, the first helical segment having afirst pitch; a second helical segment comprised of a plurality offilament segments arranged to form a second repeating pattern, thesecond helical segment having a second pitch; a plurality of strutsadjoining the first and second helical segments, wherein the struts arean integral part of the first and second helical segments.
 22. The stentof claim 21, wherein: the first and second helical segments each have acircumferential dimension parallel to the circumference of the stent;and at a plurality of points along each segment, the circumferentialdimension of that segment enlarges when the stent is expanded.
 23. Astent comprising: a first end portion; a second end portion; a generallycylindrically shaped body disposed between the first and second endportions, the body comprised of: a plurality of expandable elements,each expandable element comprising: an undulating filament segmentcomprising: a first filament portion; a second filament portion; a thirdfilament portion; a first peak having connecting the first filamentportion to the second filament portion; a first valley connecting thesecond filament portion to the third filament portion, wherein the firstvalley and first peak have substantially the same widths and wherein thefirst peak is connected to only the first and second filament portionsand wherein the first valley is connected to only the second and thirdfilament portions; and a plurality of connecting elements havingmidpoints, the connecting elements joining at least one of theexpandable elements to another of the expandable elements; and wherein afirst imaginary line connecting the midpoints of a first set of at leastthree of the connecting elements forms a first imaginary helical line inthe body of the stent and wherein a second imaginary line connecting themidpoints of a second set of at least three of the connecting elementsforms a second imaginary helical line in the body of the stent, thesecond imaginary helical line being substantially parallel to the firstimaginary helical line.
 24. The stent of claim 23, wherein the first,second, and third filament portions of at least some of the expandableelements are substantially parallel to the cylindrical axis of the bodyof the stent,
 25. The stent of claim 23, wherein the expandable elementshave the same general shape.
 26. The stent of claim 25, wherein theexpandable elements have the same general size.
 27. The stent of claim25, wherein the first, second, and third filament portions aresubstantially linear.
 28. The stent of claim 25, wherein the expandableelements are generally sinusoidal in shape.
 29. The stent of claim 28,wherein the first, second, and third filament portions are substantiallylinear.